alpha-proteobacteria

One of the five subgroups of proteobacteria, each with distinctive 16S rRNA sequences. This group contains most of the oligotrophic proteobacteria; some have unusual metabolic modes such as methylotrophy, chemolithotrophy, and nitrogen fixing ability. Many have distinctive morphological features.

beta-proteobacteria — One of the five subgroups of proteobacteria, each with distinctive 16S rRNA sequences. Members of this subgroup are similar to the alpha proteobacteria metabolically, but tend to use substances that diffuse from organic matter decomposition in… … Dictionary of microbiology